Import template/android/ as part of the top level build (#32124)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/32124

This Diff adds `template/android/` as part of the top level build as an included
build. This means that the Android template will be loaded inside Android studio and it
will be easier to invoke tasks directly there.

I'm also bumping Gradle to 7.0.2 for the template.

Please note that the template relies on the `template/node_modules` folder to
work correctly, as the Gradle build is loading a file from there.
Therefore I've added a check to verify that we import the build only if `node_modules`
is available.

Changelog:
[Internal] [Changed] - Load template/android/ inside the build.

Reviewed By: ShikaSD

Differential Revision: D30672845

fbshipit-source-id: 7253296b54e1fde7448e0e170d59b244ed9ec8fb